This invention relates to power MOSgated devices and more specifically relates to a novel structure having an increased channel width per unit area and a reduced polysilicon gate resistance.
Power MOSgated devices are well known and may be power MOSFETs, IGBTs, GTOs and other devices using a MOSgate for conduction control. At low voltages, a topology has been used in which a plurality of elongated base stripes which contain source regions form vertical conduction channels which conduct when the channel regions defined by the sources within their respective bases are inverted by a MOSgate. The MOSgate structure usually consists of thin gate oxide and a conductive polysilicon gate overlying the oxide and atop the invertible channel regions.
Such structures are shown in copending Ser. No. 09/038,453 filed Mar. 11, 1998 (IR-1455). It is desirable in such structures to bring the stripes close together to increase their density and, thus the channel width per unit area. The space needed to make electrical contact from the source electrode to the source and base region of each base strip requires a minimum possible base strip spacing. It is known to make a remote source/base contact to enable a closer packing of trench topology type strips, as shown for example in copending application serial no. (Not Yet Filed) (IR-1461). It is also known to use a planar topology strip arrangement with a non-linear shape to create closely spaced strip sections with intermittent widely spaced contact sections, as shown in U.S. Pat. No. 5,703,389, dated Dec. 30, 1997. That arrangement, however, restricts polysilicon gate current to flow along the axis of the strips.
It is also known to use, enlarged base regions for contact to base strips having narrow segments, as in U.S. Pat. Nos. 4,833,513 and 5,521,410, but these do not provide a minimized spacing between narrow base segments.
It would be desirable to provide a planar topology strip base design for MOSgated devices to increase channel width per unit area while allowing the polysilicon gate charging current to flow in any axis.